1. Field of the Invention
The present invention generally to linear actuators and, more particularly, to linear actuators used for moving a spindle by a driving source, such as a motor, and for minutely positioning a work.
2. Description of Related Art
Automatic alignment apparatuses in the optical industry and associated industries, inclusive of optical fibers, use a fine positioning device for minutely positioning a work. Some of the minute positioning devices known in the art use a driving source, such as a motor, to move a driving member.
Japanese Utility Model Laid-Open No. 37708/1987 (hereinafter JP 37708/1987) and U.S. Pat. No. 4,496,865 (hereinafter U.S. ""865) disclose minute positioning devices that use a motor to move the spindle.
The linear actuator described in JP 37708/1987 is a micrometer head. The micrometer head includes a cylindrical spindle provided inside a main body and having a female screw on its inner circumference, a driving shaft rotatably supported by the main body and having a male screw meshing with the female screw of the spindle, a motor having a rotor that is juxtaposed with the spindle, and a gear train for transmitting the rotation of the rotors of the motor to the driving shaft.
In such a construction, when the motor is driven for rotation, the gear train transmits the rotation of the rotor to the driving shaft. The rotation of the driving shaft, in turn, moves the spindle in the axial direction.
The linear actuator described in U.S. ""865 includes a main body, a spindle meshed with the main body by a screw and arranged movably from one of the end sides of the main body in an axial direction, and a motor arranged at the other end of the spindle and having rotors fixed thereto so as to be capable of integrally rotating. A groove is defined in the axial direction inside the main body and the motor has a protuberance meshing with the groove. Due to engagement between the groove and the protuberance, the motor can move in the axial direction of the spindle while its rotation is restricted. When the U.S. ""865 rotor turns, the spindle rotates and moves in the axial direction due to its engagement with the main body.
Unfortunately, the constructions taught by the aforementioned prior art devices suffer from disadvantages that limit their usefulness. For example, in the assembly of JP 37708/1987, the spindle and the motor are juxtaposed. Therefore, to transmit rotation of the rotor to the spindle, a gear mechanism must be provided therebetween. Hence, a large space in the vertical direction relative to the spindle must be provided to accommodate the motor and the gear train. Consequently, the size of the linear actuator is unavoidably large.
In the assembly of U.S. ""865, the spindle and the rotor are directly coupled. To restrict rotation of the motor, therefore, it is necessary to engage the main body with the motor by engaging the groove with the protuberance. Since the motor, too, moves integrally with the spindle, a space for accommodating cables of the motor must be provided over the moving range of the motor. This construction, too, increases the size of the linear actuator. Also, since the cables undergo extension and contraction as the motor moves axially, they are likely to be damaged.
Furthermore, since force for moving the motor itself, in addition to the force for rotating the spindle, is necessary, the motor output must be increased.
It is therefore an object of the invention to provide a linear actuator that eliminates or minimizes the problems found in the prior art technologies. It is a further object of the invention to provide a linear actuator of reduced size and simple construction.
The present invention is directed toward a linear actuator having a driving member fixed by a screw to a main body so as to be capable of moving in an axial direction; displacement detection means for detecting an amount of movement displacement of the driving member in the axial direction; rotation driving means disposed on one of the end sides of the driving member on the same axis as that of the driving member; and a transmission mechanism for transmitting turning force of the rotation driving means to the driving member. The transmission mechanism includes a first rotary member fitted to one of the end sides of the driving member and integrally rotating with the driving member. A second rotary member is fitted to a rotary shaft of the rotation driving means and connection rods for transmitting rotation of the second rotary member to the first rotary member. The connection rods are arranged parallel to, but radially displaced from, an axis of the driving member, and are connected to one of the first rotary member and the second rotary member, and engaged with the other of the first and second rotary members so as to be capable of sliding in an axial direction while transferring rotary motion between the first and second rotary members.
In further accordance with the present invention, the transmission mechanism transmits the turning force of the rotation driving means to the driving member, and the driving member is thereby rotated. The driving member is moved in the axial direction via engagement of the main body with the driving member, and the displacement detection means detects the amount of displacement of the driving member in the axial direction. Therefore, when the rotation driving means is controlled on the basis of the displacement amount of the driving member in the axial direction detected by the displacement detection means, movement of the driving member can be controlled with high precision.
In the transmission means, the turning force of the rotation driving means turns the second rotary member through the rotary shaft. Next, the connection rods transmit rotation of the second rotary member to the first rotary member, and the first rotary member is rotated. Subsequently, since the driving member and the first rotary member are connected for common or integral rotation, the driving member is rotated. Due to engagement between the main body and the driving member, the driving member is moved in the axial direction.
The connection rods are disposed parallel to the axis of the driving member and on axes different from the axis of the driving member. Therefore, the connection rods are rotated with the axes of the driving member and the rotation driving means as the center axis of rotation. Rotation of the second rotary member is transmitted to the first rotary member and to the driving member through rotation of the connection rods with the axis of the driving member as the center.
The connection rods are engaged with one of the first and second rotary members and are connected to the other of the first and second rotary members so as to be capable of sliding in the axial direction. Therefore, engagement between the first rotary member, connection rods, and second rotary member is maintained through sliding of the connection rod even when the interval or space between the first and second rotary members changes. Consequently, rotation is transmitted from the second rotary member to the first rotary member through the connection rod even when the interval or space between the first and second rotary members changes. In other words, even when only the driving member moves while the position of the rotation driving means is kept constant or unchanged, rotation can be transmitted from the rotation driving means to the driving member.
As a result, in the present invention it is not necessary to define the groove and the protuberance that have been required in the linear actuator structure according to the prior art wherein the rotation driving means moves with the driving member. In the present invention, a space for accommodating the cables in a distance corresponding to the moving distance of the rotation driving means is not necessary. Therefore, the risk of damaging the cables as a result of extension and contraction is eliminated.
Moreover, in the linear actuator according to the prior art, the main body and the rotation driving means are interconnected with each other by the engagement means, or the driving member and the rotation driving means are integrated with each other. Therefore, in the prior art it is impossible, or at best very difficult, to exchange or replace the rotation driving means. However, in the present invention, since the rotation driving means is merely fitted to the second rotary member, it can be easily exchanged and replaced by other rotation driving means in accordance with the intended application.
When the first rotary member and other members (connection rods, second rotary member, rotation driving member) are fitted to the driving member in the linear actuator for manually rotating the driving member, the linear actuator can be easily changed to a linear actuator using the rotation driving means.
In the linear actuator according to the present invention, the connection rods are slidably secured to one of the first and second rotary members so as to be capable of sliding in the axial direction. According to this construction, even when the interval or space between the first and second rotary members changes, the engagement between the first and second rotary members is maintained through sliding of the connection rods. Therefore, rotation can be transmitted from the second rotary member to the first rotary member even when the interval between them changes.
In accordance with the present invention, an alternative second rotary member includes a first member, a second member, and a spring member. The first member is secured to the rotation driving means, and the second member is secured to the first rotary member by the connection rods. The connection rods are connected to and integrally extend from the second member. The spring member interconnects the first and second members and serves to absorb any misalignment between the axis of the rotation driving means and the axis of the driving member.
The linear actuator according to the invention also has a knob rotating integrally with the rotary shaft of the rotation driving means. The knob is provided on the rotation driving means on the side opposite the driving member. When the knob is manually turned to rotate the rotary shaft of the rotation driving means, the transmission mechanism transmits this rotation to the driving member. Therefore, the driving member can be manually moved. Because the driving member can be manually moved without relying on the rotation driving means, excellent operational results can be obtained, especially when the position of the driving member is minutely adjusted.
In further accordance with the present invention, the linear actuator includes a third rotary member moving and rotating integrally with the driving member, a transparent member provided to a part of the side surface of the main body corresponding to the moving range of the third rotary member, a scale formed in the moving direction of the third rotary member, and another scale formed on the circumferential side surface of the third rotary member. When the driving member moves in the axial direction while rotating, the third rotary member, too, moves integrally and is rotated. Since the transparent member is provided to the side surface of the main body corresponding to the moving range of the third rotary member, the movement of the third rotary member can be visually confirmed through the transparent member, and the moving displacement amount of the driving member can be read from the scale provided on the main body. Further, the amount of rotation of the driving member can be read from the scale provided on the circumferential side surface of the third rotary member. Since the amount of rotation of the driving member is converted to the movement displacement amount in the axial direction from the pitch of the screw, minute displacement of the driving member can be read from the scale of the third rotary member in addition to the scale of the main body.